Owing to the rapid development of multimedia technology and display technology, display devices have become widely used as electronic devices. Accordingly, more and more display devices employ a touch panel.
A touch panel recognizes the coordinates of a point on a screen touched by a finger and/or an object and processes a specific function by executing a software command corresponding to the touched point, which obviates the need for an additional input tool and/or input device such as a keyboard, a mouse, and the like.
There are largely two types of touch panels, resistive touch panel and capacitive touch panel. To implement a capacitive touch panel, first electrodes serving as driving lines (for Transmission (Tx)) and second electrodes serving as sensing lines (for Reception (Rx)) should be configured independently. The first and second electrodes may form patterns on the same or different layers. Intersections between the first and second electrodes, each intersection forming one pair of (X, Y) coordinates, should be isolated from one another by means of insulators.
Depending on their operation principles, touch panels may be categorized into an InfraRed (IR) type, a Surface Acoustic Wave (SAW) type, an ElectroMagnetic (EM) type, and an ElectroMagnetic Resonance (EMR) type.
From the perspective of structure, a touch panel may be configure as one of a glass Touch Screen Panel (TSP), a Glass Film Film (GFF) TSP, a hybrid Glass-One Film (G1F) TSP, and a G2 (integrated cover-glass) TSP. The glass TSP has a glass sensor inserted between a cover glass and a display panel. Despite excellent optical characteristics compared to a film-based TSP, the glass TSP becomes less popular due to a heavy, thick substrate and high cost. The G1F TSP is fabricated by depositing one layer of Indium Tin Oxide (ITO) on the rear surface of a window, patterning the ITO layer, and then attaching one layer of ITO on the other axis. In the G2 TSP, a touch sensor is implemented by depositing two X-axis and Y-axis layers of ITO on the rear surface of a window. That is, the G2 TSP has an integrated structure in which electrodes are formed directly on a cover glass without an additional sensor layer. Due to the absence of an additional glass or film substrate, the G2 TSP boasts of excellent optical characteristics and low material cost and makes it possible to implement a thin, lightweight substrate. Therefore, the G2 TSP is regarded as an ideal touch panel structure.
For example, the first and second electrodes may be formed of ITO composed of indium oxide (In203) and tin oxide (SnO2). The ITO has high transmittance, despite high resistivity compared to metals such as copper or silver.
FIGS. 1A to 1D sequentially illustrate an operation for fabricating a touch panel according to the related art. Referring to FIG. 1A, a window 1 is fabricated and an ink-printed layer 2 is provided on the top surface of the window 1. A reflective coating layer 3 is attached onto the top layer of the ink-printed layer 2 and a first electrode 4 is provided on the top surface of the reflective coating layer 3. Referring to FIG. 1B, a first pattern is formed. Referring to FIG. 1C, a second electrode 5 is provided on the top surface of the first electrode 4 and a metal electrode layer 6 is deposited on the top surface of the second electrode 5. Referring to FIG. 1D, a second pattern is formed by etching.
When the first pattern is formed, the first electrode is removed from an invisible area of the window. The window is divided into a visible area visible to a user and the invisible area corresponding to the remaining area except for the visible area. That is, the touch panel includes a visible area visible to the user and an invisible area invisible to the user.
In the touch panel of the related art, a metal electrode layer formed of silver (Ag) used in a current process has high electrical conductivity but is vulnerable to breakage due to low physical strength. Since the metal electrode layer is positioned on the top layer of the touch panel, the metal electrode layer is vulnerable to breakage during transfer and post-processing. Moreover, the touch panel of the related art experiences a chemical change at the metal electrode layer due to introduced moisture in a high-temperature, high-humidity environment. As a result, the metal electrode layer is discolored and suffers from degraded electrical characteristics and weakened adhesion.
Thus, it may be concluded that the metal electrode layer of the related art is easily broken due to low physical strength, is vulnerable to a chemical change due to exposure to the outside, and has degraded electrical characteristics and weakened adhesion.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.